In recent years, the field of “vacuum microelectronics” has experienced tremendous growth. Vacuum microelectronics is the science of building devices that operate with electrons that are free to move in a vacuum based on the ballistic movement of the electrons in the vacuum. This enables higher electron energies than are possible with semiconductor structures, so vacuum microelectronic devices can operate at higher frequencies and higher power in a wider temperature range, as well as in high radiation environments. By contrast, solid-state semiconductor microelectronics have carriers (e.g., electrons and holes), which have their movement impaired by interaction with the lattice structure of the semiconductor substrate.
One way of obtaining electrons for vacuum microelectronics devices is by field emission or “cold emission,” using a typical Spindt emitter. A Spindt emitter includes a substrate with small cones fabricated into its surface designed to emit electrons from their tips. Alternate geometric configurations such as wedges or “volcano” configurations have also been used. Each cone, or other design, has a concentric aperture etched from the substrate surrounding the cone. This aperture has a conductive gate film deposited on its surface so that an array of cones functions as a field emission source of electrons when a positive potential is applied to the gate relative to the tips of the cones. Once free of the confining tip, the electrons traverse the vacuum space and can be used for applications ranging from microwave communication to lighting flat panel displays.
Unfortunately, Spindt emitters are very difficult to fabricate. For example, many issues affect the etching or formation of the cones, or other shapes of the Spindt emitter. Fabrication difficulties include, for instance, forming a cone with a precise tip, uniformity of the cones within an array, spacing between cones of the array, and scaling of the cone forms (i.e., obtaining a 1:1 base diameter-to-cone height ratio).
Another type of emitter that produces electrons is a thin-film edge field emitter. This type of emitter includes a substrate, such as that used as the base of an integrated circuit, in which thin-film layers of material are deposited upon, using a chemical beam deposition (“CBD”) process for example, and desired areas are etched out of these layers to form an area where electrons may be extracted. Similar to Spindt emitters, thin-film edge field emitters are difficult to manufacture since precise designs are required, therefore, it is difficult to create these type of emitters with reproducibly designed emitter surfaces. Consequently, an electron source that overcomes these problems is desirable.